A Coupled Differential Scanning Calorimetry and X-ray Study of the Mesomorphic Phases of Monostearin and Stearic Acid in Water

Differential scanning microcalorimetry coupled to Synchrotron small angle X-ray scattering (SAXS) was used to characterize the mesomorphic phases of monostearin - a series of dispersions of monostearin and stearic acid (95:5 w/w.) in alkaline water were prepared in the range 5-90% (w/w). Samples were subjected to both melting and cooling regimes from 45 to 81 at 2 degrees C/min in a Microcalix machine (an X-ray sample chamber with microcalorimetry capabilities), while X-ray spectra and the microcalorimetric trace were being collected simultaneously. Using these two techniques, two-dimensional phase diagrams of the mesomorphic phases (lyotropic and thermotropic liquid crystalline phases as well as the crystalline, hydrated get phases) of monostearin was created, one for heating and one for cooling, and the typical X-ray diffraction pattern for each of the phases was identified. Polarized light microscopy was also used in ail attempt to differentiate and identify the mesomorphic phases. Furthermore. the largest. d-spacings (which includes the thickness of the water domain and the lipid bilayer) for each of the different monostearin concentrations were plotted at 73 degrees C during healing and when cooling, to better understand the water binding capacity of the different mesomorphic phases. This information will provide guidance for the use of these unique phases in food and pharmaceutical applications.